Under-gassed 300BLK AR help

[ACC]

I recently built a new AR SBR in 300BLK. It has a carbine-length gas system and is under-gassed, even when run with a suppressor. It will eject the casing, but not pick up the next round.

I need to increase the gas flow on this gun to get it to run well. Do I do this by drilling the gas port hole on the barrel? Drilling the gas block?

Please advise.

 

[rvb]

I recently built a new AR SBR in 300BLK. It has a carbine-length gas system

aren't most 300blk pistol-length gas systems? I'm no 300blk expert/fan, but you might be "behind the curve" already w/ a carbine length system...

-rvb

 

[rvb]

It will eject the casing, but not pick up the next round.

will it lock the bolt back on the last round?

I need to increase the gas flow on this gun to get it to run well. Do I do this by drilling the gas port hole on the barrel? Drilling the gas block?

which is smaller, the barrel port or the gas block port? on a 223 or 308 it's always the barrel, but again, sorry, no 300 expert. running heavy buffers?

-rvb

 

[ACC]

aren't most 300blk pistol-length gas systems? I'm no 300blk expert/fan, but you might be "behind the curve" already w/ a carbine length system...

-rvb

most are pistol length systems, but this was a specialty build to be always run suppressed and it had to be carbine length. Many people run carbine length gas systems with a suppressor in 300blk

 

[DanVoils]

I recently built a new AR SBR in 300BLK. It has a carbine-length gas system and is under-gassed, even when run with a suppressor. It will eject the casing, but not pick up the next round.

I need to increase the gas flow on this gun to get it to run well. Do I do this by drilling the gas port hole on the barrel? Drilling the gas block?

Please advise.

What is the length of the barrel? Usually they are pistol length gas systems.
Does the lower work properly on other uppers?
Dan

 

[ACC]

will it lock the bolt back on the last round?



which is smaller, the barrel port or the gas block port? on a 223 or 308 it's always the barrel, but again, sorry, no 300 expert. running heavy buffers?

-rvb

Does not lock back on last round. I watched and could see that the bolt does not fully retract and just barely gets the casing out. Not running a heavy buffer. Not sure which gas port is smaller. Have not pulled the gas. Lock off yet.

 

[masterdekoy]

There's a lot of variables to consider. Supers or Subs? I assume subs if you are running suppressed. Have you contacted the manufacturer to see what their recommendation is?

 

[Mgderf]

I hate to be "that guy", but are you absolutely positive the barrel and gas block are in perfect alignment?

 

[Trigger Time]

Cool story bra

 

[Sling10mm]

Manufacturer of the barrel/upper?
Barrel length?
Ammunition being used?
Buffer being used?

I believe the opening in the gas block should be larger than the port in the barrel, but I would try other options (check block alignment, different ammo, etc.) before drilling it. I don't understand your comment about the carbine gas. Why does it have to be carbine length to be suppressed all of the time?

 

[throttletony]

most are pistol length systems, but this was a specialty build to be always run suppressed and it had to be carbine length. Many people run carbine length gas systems with a suppressor in 300blk

There's a lot of variables to consider. Supers or Subs? I assume subs if you are running suppressed. Have you contacted the manufacturer to see what their recommendation is?

Manufacturer of the barrel/upper?
Barrel length?
Ammunition being used?
Buffer being used?

I believe the opening in the gas block should be larger than the port in the barrel, but I would try other options (check block alignment, different ammo, etc.) before drilling it. I don't understand your comment about the carbine gas. Why does it have to be carbine length to be suppressed all of the time?

As above - whats the barrel length? Ive heard of (mostly??) folks running suppressed with pistol length gas system - though itz been a yr since i built my 300blk pistol.
I suspect either: too short of dwell time, way underpowered ammo, misalignment of gas block, blockage in gas port or tube, or overall too short of barrel to use carbine length gas (yes, i repeated that one twice.. just in case the barrel is like 9" or something).

Also worth repeating. I have not heard of a preference for shooting carbine length gas if suppressed. MAYBE for a rifle length gun 16+ barrel, but not on SBR/pistol...

 

[ACC]

OK....I will try to reply to all the questions.

1. Barrel is 10.5"
2. It is an Anderson Manufacturing barrel and a Dez Arms Clamp-on FSB.
3. FSB is installed correctly and in alignment as best as I can tell.
4. Shooting freedom munitions subsonic 300BLK
5. Not saying it is PREFERABLE to run a carbine length gas system. I am saying that carbine length gas systems with 300BLK pretty much only work if you are shooting them suppressed. I never expected the gun to run unsupressed with subsonic ammo. But my research said that it should run fine if running suppressed.
6. Lower works fine with other uppers.

 

[Trigger Time]

I have built 5 300 blackout pistols for myself. All of them 8.5" down to 8" barrels with pistol gas. They've ALL ran flawlessly suppressed and unsuppressed. I also have 2 BCM 300 blackout factory uppers that are 9" and also pistol gas. Also run both ways flawless.
barrels brands used in personal builds: cmmg, BA Hansen, aero, noveske

maybe this info will help you

 

[DanVoils]

My 8" is obviously a pistol length gas system and works fine with multiple configurations: suppressed/unsuppressed with super and sub sonic. It uses a standard buffer weight and spring. I'm thinking the 10.5" needs a pistol length gas system.
Are the other uppers the same caliber and/or length? What works for a 5.56 16" may not work with a .300 blk 10.5" subsonic suppressed. I presume you're running a standard buffer weight and spring.
Instead of buying a bunch of buffers and springs I could meet you at a range and you could try your upper on my lower and vice-versa. That would eliminate a lot of guessing and narrow it down.
Dan

 

[throttletony]

OK....I will try to reply to all the questions.

1. Barrel is 10.5"
2. It is an Anderson Manufacturing barrel and a Dez Arms Clamp-on FSB.
3. FSB is installed correctly and in alignment as best as I can tell.
4. Shooting freedom munitions subsonic 300BLK
5. Not saying it is PREFERABLE to run a carbine length gas system. I am saying that carbine length gas systems with 300BLK pretty much only work if you are shooting them suppressed. I never expected the gun to run unsupressed with subsonic ammo. But my research said that it should run fine if running suppressed.
6. Lower works fine with other uppers.

Thanks for info.
Yeah, check gas port alignment and size.
Also, have you tried this same bolt carrier + buffer + spring in a 5.56 rifle?? I wonder if the gas key (or something??) is dragging or out of spec.

 

[Trigger Time]

Almost 90% of the time it's a gas issue from the front or to the back to the bcg.
if you know someone that has a light weight bcg try that. If you live in Indy you can come borrow
My spikes out of my crusader. It MAY make the difference. If so it will be cheaper to get one of those than to get a new barrel.

 

[Bfish]

Is it not running with subs or not running with supers? If it's not running with supers you really have a problem! Could be with that length gas system you may have to enlarge it. A buddy of mine had to do that on a build he couldn't get to run properly. I think centurion arms did it, but now it runs super sweet.

 

[neraph]

I'm just going to throw my experience out there:

I have a 16" barrel with carbine gas. It will not cycle with subsonic loads that use H110. Accurate 1680 is the only powder that I've gotten to work. Obviously, I'm handloading, but I do recall that Remington 220gr subsonic cycled without problem.

Even Shorter version: 300 blackout with carbine gas is picky about ammunition. Try something else.

 

[Ericpwp]

My 10.5 is pistol gas fwiw.

 

[M67]

300blk barrels are usually a pistol length system for a reason. At a carbine system, usually the pressure has tapered off too much to be reliable, especially with subs